The treating and processing of bone material is becoming increasingly important as the demand for bone implants and grafts (hereinafter “bone grafts” or “grafts”) rises. Bone material must be processed properly; otherwise, disastrous consequences may result from implants of improperly processed bone material into a host. Such disastrous consequences include but are not limited to: a host's immunogenic response to the graft, a host's rejection of the bone graft altogether, the possible transfer of diseases and infectious agents from the donor to the host due to unclear bone grafts, prolonged recovery time for the host, and multiple avoidable operations on the host to remove an improperly processed bone graft. To avoid such problems, bone material must be properly processed to selectively eliminate fats, proteins, donor cells, viruses, bacteria, and the like, before the bone material can be successfully implanted into the host.
Conventionally, the processing of bone material includes a number of steps. FIG. 1 shows a flow chart 100 of the steps using the conventional method of processing bone material as disclosed in the prior art. In the step 101, the bone material is obtained from a donor. In the step 110, the bone material is degreased by placing it into a container of acid or acetone. In the step 120, the bone material is rinsed using a rinse medium, such as a water bath. Next, in the step 130 the bone material is oxidized, where the bone material is sterilized from viruses and the like. Usually, this oxidizing step requires the bone to be treated with hydrogen peroxide. In the step 140 the bone material is rinsed again. In the step 150, the bone material is treated with a base for protein removal. In the step 160, the bone material undergoes yet another rinse. Then, in the step 170, the bone material is dried using some type of alcohol or acetone. Optionally, in the step 180, the bone material is treated with gamma radiation. In the step 190, the final product resulting from the conventional method is a white, bleached sterile demineralized bone matrix, which oftentimes has denatured collagen and lacks bone morphogenic proteins (BMPs), which are growth factors key to bone osteoconductivity and osteoinductivity.
The conventional method falls short in providing the ideal bone graft. The ideal bone graft is one that is both osteoconductive and osteoinductive. Osteoconductivity and osteoinductivity are two vital mechanisms for the regeneration and rebuilding of bone. Osteoinductivity refers to the ability to build, heal and regenerate bone in humans, and this is realized through active recruitment of host stem cells from surrounding tissue, which differentiate into bone-forming osteoblasts. Growth factors, particularly BMPs, aid and stimulate bone osteoinductivity. Collagen found inside the bone material provides an exceptional osteoinductive substrate for bone formation. To be osteoinductive, the ideal bone graft must contain undamaged BMPs and collagen. In contrast with osteoinductivity, osteoconductivity refers to the ability of a bone graft to form a scaffold or a structure on which the host's cells are able to form new bone. Thus, the ideal bone graft is both osteoinductive and osteoconductive, since such a graft allows for new bone to form at the implant site and further provides structural support for the formation and incorporation of the new bone.
The disadvantages of the conventional method are several-fold. First, the conventional method requires several separate processing chambers for the bone material to be processed, using a multitude of chemicals, some of which are toxic. For instance, acetone can be used for the degreasing step, step 110, and the drying step, step 170, of the conventional method, and yet in some countries, acetone is a prohibited processing agent due to its toxicity. Second, the conventional method can be expensive, labor-intensive, and time-consuming, given the numerous steps and various processing agents that are required. Also, the number of steps required by the conventional method increases the likelihood that some type of error will occur and the bone material will be improperly processed. Further, the oxidizing step, step 130, of the conventional method destroys the BMPs in the bone, leaving a sterile mineral matrix. Finally, the base step of the conventional method, step 150, can denature collagen and destroy BMPs. By denaturing collagen and killing growth factors, such as the BMPs, the conventional method unfortunately can result in a decrease of both the osteoconductivity and osteoinductivity of the bone material, which translates into a longer time for the bone material to incorporate properly into the host body or a complete rejection of the bone material.
In U.S. Pat. No. 5,725,579, issued to Fages et al, entitled “Process for Treating Bone Tissue and Corresponding Implantable Biomaterials,” issued Mar. 10, 1998, it was disclosed that the degreasing step, step 110, and the rinse step, step 120, of the conventional method (FIG. 1) can be replaced by a single step of treating a bone material with supercritical fluid. However, under Fages, the remainder of the conventional method steps, namely, the steps 130, 140, 150, 160, and 170 (FIG. 1), must follow after treating the bone material with supercritical fluid, for the cleaning process to be completed.